Synthesis and characterization of heteroleptic titanium MOCVD precursors for TiO₂ thin films

Abstract

Heteroleptic titanium alkoxides with three different ligands, i.e., [Ti((OPr)-Pr-i)(X)(Y)] (X = tridentate, Y = bidentate ligands), were synthesized to find efficient metal organic chemical vapor deposition (MOCVD) precursors for TiO2 thin films. Acetylacetone (acacH) or 2,2,6,6-tetramethyl-3,5-heptanedione (thdH) was employed as a bidentate ligand, while N-methyldiethanolamine (MDEA) was employed as a tridentate ligand. It was expected that the oxygen and moisture susceptibility of titanium alkoxides, as well as their tendency to form oligomers, would be greatly reduced by placing multidentate and bulky ligands around the center Ti atom. The synthesized heteroleptic titanium alkoxides were characterized both physicochemically and crystallographically, and their thermal behaviors were also investigated. [Ti((OPr)-Pr-i)(MDEA)(thd)] was found to be monomeric and stable against moisture; it also showed good volatility in the temperature window between volatilization and decomposition. This material was used as a single-source precursor during MOCVD to generate TiO2 thin films on silicon wafers. The high thermal stability of [Ti((OPr)-Pr-i)(MDEA)(thd)] enabled the fabrication of TiO2 films over a wide temperature range, with steady growth rates between 500 and 800 degrees C.